Glucagon-Like Peptide 1 (GLP-1) is a 37 amino acid peptide that is secreted by the L-cells of the intestine in response to food ingestion. It has been found to stimulate insulin secretion (insulinotropic action), thereby causing glucose uptake by cells and decreased serum glucose levels (see, e g., Mojsov, S., Int. J. Peptide Protein Research, 40:333–343 (1992)). These and other effects make GLP-1 an attractive candidate for the treatment of type 2 diabetes.
Thus far, however, efforts to commercially develop a GLP-1 drug candidate have been hampered by numerous obstacles. For example, the development of native GLP-1 compounds has not been feasible because they are rapidly degraded by endogenous proteases and thus, have an extremely short in vivo half-life. Although analogs with longer half-lives have been studied, these analogs have been difficult to develop commercially due to stability problems encountered during the manufacturing process.
One particular analog that has been studied is Val8-GLP-1(7–37)OH. See U.S. Pat. No. 5,977,071. This analog has a potency similar to that of the truncated native GLP-1 peptides GLP-1(7–36)NH2 and GLP-1(7–37)OH but has a longer circulating half-life. Val8-GLP-1(7–37)OH, however, exists in at least two different forms. The first form is physiologically active and dissolves readily in aqueous solution whereas the second form is substantially insoluble in water at physiological pH and is inactive. Further, Val8-GLP-1(7–37)OH has a tendency to aggregate and convert to an inactive insoluble form during manufacturing. Thus, efforts to improve the properties of this compound have continued. Discovery efforts have focused on improving the stability of the compound in the context of large scale manufacturing as well as formulation development without compromising the biological activity.
The present invention encompasses a Val8-GLP-1 analog having such improved properties. The invention encompasses the discovery that an amidated form of Val8-GLP-1(7–37)OH known as Val8-GLP-1(7–37)NH2 has increased in vitro potency compared to Val8-GLP-1(7–37)OH (the acid form) and has superior stability properties that facilitate large-scale manufacturing and make it an ideal candidate to formulate as a solution for continuous infusion or as a crystal suspension for subcutaneous administration.
Although native GLP-1 is amidated in vivo, there has been no motivation to study amidated analogs because both native isoforms appear to have identical biological effects and amidated peptides are perceived as more difficult to make biosynthetically. In addition, unlike the amidated analog encompassed by the present invention, amidation of the native molecule actually involves replacement of the C-terminal glycine-OH with NH2 resulting in GLP-1(7–36)NH2. Further, the corresponding Val8-GLP-1(7–36)NH2 analog, disclosed in U.S. Pat. No. 6,133,235, actually turns out to be slightly less potent than the acid form.
Thus, it is surprising that Val8-GLP-1(7–37)NH2 has increased stability as a formulated compound as well as increased stability in the context of manufacturing processes over the acid form of the analog. Even more surprising is the increased potency compared to the acid form or the truncated amide form of the analog.